The structure of an extended area collector according to prior art (eg. see United Kingdom Patent Specification GB 2100058A), is illustrated in FIG. 1.
The structure, as shown, comprises an array of pyroelectric detecting elements 1, each of which is mounted in thermal contact with a corresponding collector 3, formed of thermal absorbing material. Thermal contact is assisted by an intermediary layer 5 of highly conductive material. As shown, these components 1,3 and 5 are retained within supporting layers 7, 9 of thin polymer film. The collector 3 collects and absorbs radiation over an area larger than that of the detector element 1 and transfers the energy absorbed into the thermal detector 1 by thermal conduction. The temperature rise of the detector element 1 is enhanced compared with either a detector element of identical size without a (XAC), or an hybrid composite with a detector element of area equal to that of the XAC, provided that the thermal capacitance of the XAC plus detector structure is lower than that of the detector element above (for either case), assuming that the thermal conduction process is not itself limiting.
In the prior art structure (FIG.1) the thermal conduction path is via a thin metal layer (not shown) of high thermal conductivity (eg. a metal layer of Al, Cu, Ag or Au) that is deposited onto one of the flexible polymer films 7 and 9 that support the detector element 1. The prior art structure is suited to relatively coarse pitch thermal detectors of intermediate performance, albeit it has a performance considerably improved over the equivalent detector without an XAC. However, the prior art structure presents problems at the finest thermal detector pitches and where the highest degree of thermal isolation between adjacent elements and between detector and environment (eg. the silicon readout circuit chip in a thermal detector - silicon hybrid device), is required, since a requirement conflict then arises between thermal radiation collection and thermal isolation. These problems arise because, in the prior art structure, the XAC absorber 3 and the thermal transfer layer 5 are both placed on, and, in contact with, the polymer support film 7 that, while providing mechanical integrity for the structure, also provides a dominant thermal path between the elements 1 and to any adjacent heatsink structures. The degree of thermal isolation of the prior art structure and the extent of thermal cross-talk is controlled by the distance apart of the edges of the collector structure 3, rather than by the separation of the edges of the adjacent detectors 1.